The PM Process
P/M process is basically a three-step technology that is
feasible for both high-volume and low-volume production,
making it the right choice for a wide variety of industries
In this first stage, the base metal is fed into a large
blender and mixed with a small amount of die lubricant and
the desired alloying agents. The result is a completely
homogeneous material ready for compacting.
On a simple part, compacting takes place in three basic
movements. First, blended metal powder is gravity-fed via
an automatic shuttle into the die which has been mounted
in a press. The upper punch then enters the die and compacts
the material against the lower punch at room temperature
and pressures generally ranging from 20 to 60 tons per square
inch. Finally, the upper punch retracts out of the top of
the die and the lower punch moves upward to eject the "green"
pressing cycle may be somewhat more complex depending on
the number of different levels and complexity in the part.
These pre-sintered green parts are relatively fragile, but
are strong enough to be handled and transported to the sintering
Generally, the pressed parts are placed on a continuous
loop belt furnace and slowly moved through the sintering
chamber. Temperature and speed of the sintering depends
on the material being sintered, though most iron-based materials
remain in a 2,000 degree Farenheit to 2,100 degree protective
atmosphere hot zone for about 30 minutes.
brings the part to a temperature well below its melting
point but hot enough to cause the chemical bonding of the
parts are then allowed to cool gradually and are frequently
ready for shipping at this point. However, some secondary
processes may be necessary to finish the part and bring
it to within the customer's specifications.
P/M parts may be repressed, impregnated, machined, tumbled,
plated, or heat treated following sintering if special properties
are required. Repressing effects densification and dimensional
control; impregnation makes bearings self-lubricating or
may be used to improve machinability, to seal parts gas
or liquid tight, or prepare the surface for plating.
is used to improve the strength of ferrous structural parts,
and heat treating can improve strength and hardness and
make the surface wear-resistant. Machining is done to install
set or assembly screws, to form undercuts not possible with
punch and die tooling, or to attain exact tolerances. Finishing
accomplishes a range of tasks, from removing sharp edges
through deburring to burnishing for size control or welding
to make assemblies from two or more parts. Finishing can
also include plating for corrosion resistance and to improve
surfaces, or shot peening to improve surface fatigue life.